currently doing a pretty massive lighting build in terms of area and around 210 seconds into the build 7 of my cores dropped out with core 0 only being active the entire build took around 12 minutes, my cpu isnt overclocked, 2600k 3.4(i think maybe 3.2) ghz
why would it just drop cores 1 through 7? the map area is around 250,000 units squared XY by around 50,000 Z with the lightmass volume as big as this.
this is with the latest build 1171197(i think thats the build number, at least thats close to it)
Lightmass has a lot of different types of tasks and they don’t all complete at the same time. The usual offender is a single high resolution (1024 or 2048) lightmap built on production. We made some improvements a few months ago so that those high res lightmaps use all the cores for longer though. I think in this case it is calculating the volume lighting samples (which is used by movable objects to represent diffuse GI) which is taking so long, based on the size of your importance volume. You can test this by setting StaticLightingLevelScale to 2 and see how that affects the build time, if it goes down by 2-4x then that is the issue. Calculating the volume samples can be made to use all the cores with some effort. I expect we will do so shortly. Thanks for pointing this out.